Testing for Life Historical Changes in Spatial Patterns of Four Tropical Tree Species

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Abstract
(1) Spatial patterns of the mortality of tropical trees were investigated using maps of four species [Anaxagorea crassipetala, Iriartea gigantea, Pentaclethera macroloba, Socratea durissima] on an 80 .times. 80-m site of primary rainforest in Costa Rica. Using new statistical methodology, designed specifically for complete maps of individuals, models of clustering or uniformity were fitted to different size classes, and the relative uniformity of the different size classes compared. The data for the extant juveniles were then used to predict what the extant adult spatial distribution would be given random mortality of the juveniles. The actual adult distribution was compared to this hypothetical distribution to see if they were more or less uniform than predicted. (2) For three of the four species, the spatial models which fit the adults were more uniform than the models which fit the juveniles. The adults of these three species were significantly more uniformly distributed than expected from the random mortality of their extant juveniles. The fourth species had adults with a similar distribution to randomly thinned extant juveniles. (3) Post-germination survival leads toward a uniform distribution. During the lifespan of three of the four species, repulsion occurs between individuals. At small scales, clumping, when present, may be more the result of patchy dispersal of seeds or seedling germination than the patchy survival of germinated individuals.